Carburetor



0d. 11, 1966 F. w. COOK ETAL CARBURETOR 4 Sheets-Sheet 2 Filed April 29, 1963 Oct. 11, 1966 F. w. COOK ETAL CARBURETOR 4 Sheets-Sheet 5 Filed April 29, 1963 FIG.4.

FIG.

United States Patent Filed Apr. 29, 1963, Ser. No. 276,499 2 Claims. (Cl. 261-50) This invention is directed to an air valve carburetor of the type having an air and fuel mixture conduit through the carburetor body. Within the mixture conduit is mounted a manually operated throttle valve for movement between an open and closed position. Upstream from the throttle valve is mounted within the mixture conduit an air valve structure, which measures the flow of air through the carburetor to meter the fuel flowing to the engine. The presence of the air valve also provides a subatmospheric pressure in the region of the fuel nozzles to draw fuel into the mixture conduit.

In some air valve carburetors of this type, a servo motor positions the air valve in response to the air pressure drop across the air valve such that the angular position of the air valve is a measure of the air flow to the engine. The air valve is connected directly to a device for metering fuel to the engine, so that fuel flow is proportional to the air flow to the engine. With the same amount of air flow through the engine, the air valve will assume the same angular position and thus provide the same fuel fiow to the engine at wide open throttle operation under full load as at a part open throttle operation with partial load. However, for satisfactory engine operation, the engine requires a richer air-fuel mixture for maximum power than at partthrottle operation with minimum load conditions when a leaner, economy mixture is desirable. It is thus necessary to vary the relationship between the air flow and fuel flow to the engine by providing means to change this relationship in response to engine demands.

It is therefore an object of this invention to provide a novel air valve carburetor of the type described in which the air valve controls fuel metering to the engine in response to the needs of the engine.

It is a further object of this invention to provide a novel carburetor having an air valve fuel control which more closely follows the requirements of the engine to provide an optimum fuel and air mixture during engine operation.

The invention is to an air valve carburetor in which the position of the air valve of the carburetor is determined by a servo motor responsive to an air pressure drop in the mixture conduit of the carburetor. Under partly open throttle operating conditions at low speeds or low load, the manifold vacuum is comparatively high. In accordance with the invention, the high manifold vacuum conditions are sensed by the servo motor to open the air valve a greater amount. This reduces the depression in the region of the fuel nozzles to reduce fuel flow for economy operation. Under maximum power conditions of engine operation at wide open throttle the effect of manifold vacuum is substantially lost, so that the air valve position is determined by the pressure drop across the air valve alone to give the enriched air/fuel mixture needed.

FIGURE 1 is a schematic view of an air valve carburetor in accordance with the invention and showing the operation of the carburetor during cranking of the engine in cold weather.

FIGURE 2 is a schematic operational view of the carburetor of FIGURE 1 during wide open throttle operation under normal warm ambient conditions.

FIGURE 3 is a plan view partly in section of an air valve carburetor including the invention of FIGURES 1 and 2.

FIGURE 4 is a side view in elevation of the carburetor of FIGURE 3 showing a portion of an air filter and an engine manifold to which the carburetor is attached.

FIGURE 5 is a sectional view of the carburetor of FIGURE 3 along the lines 5--5.

FIGURE 6 is a sectional view of the carburetor of FIGURE 3 along section lines 66.

FIGURE 7 is an enlarged partial view of the fuel control metering rod of FIGURE 6.

FIGURE 8 is a sectional view of the carburetor of FIGURE 3 along lines 8-8.

The carburetor shown in the figures has a body cast ing portion 10, which is connected at a flanged end 12 to an intake manifold structure 13 of engine E shown in FIGURES 4 and 5. The other end of the carburetor body supports a cover casting 19 formed with an air horn section 14 mounting an air filter 15, through which air passes into the carburetor. Passing through the carburetor body from the air horn 14 are a pair of air and fuel mixture conduits 16 and 17 each opening at one end into the intake manifold 13 at 18 and through which air from the air filter passes to the engine. Mounted in the manifold ends of mixture conduits 16 and 17 are throttle valves 20 and 21, respectively, fixed to -a common throttle shaft 22 journaled for rotational movement in appropriate bearing surfaces in the carburetor body 10. Fixed to one end of the throttle shaft 22 is a manually operable lever 24 (FIGURES 3 and 6) for moving the throttles 20 and 21 from a closed to an open position. In the closed position, the throttles are across their respective mixture passages 16 and 17, as indicated in FIG- URES 5 and 8, to prevent the flow of air therethrough. The throttles may be moved from this closed position to a wide open position schematically indicated in FIG- URE 2.

Mounted upstream of the throttles 20 and 21 and across the air horn section 14 of the carburetor is an air valve 26. As indicated in FIGURE 3, valve 26 closes the air horn passage and extends across the two mixture passages 16 and 17. A pair of apertures and 27 extend inwardly from one edge of the air valve to provide clearance with a pair of nozzle bars 80, when the air valve is opened. Air valve 26 is fixed eccentrically to a shaft 28 journaled in the carburetor body for rotational movement. Shaft 28 extends through the carburetor substantially parallel to the throttle shaft 22. The eccentric mounting of valve 26 is optional as the valve 26 may be balanced by a symmetrical mounting.

A short lever arm 30 (FIGURES 3 and 5) is fixed to and extends from the air valve shaft 28. Lever arm 30 is loosely connected to one end of an actuating rod 32, the other end of which extends through a passage 33 (FIG. 5) in body casting 10 and is fired to a backing plate 34 of a diaphragm assembly 36 of a servo motor 39. The diaphragm assembly consists of a flexible diator body.

phragm 38 of rubber or appropriate material, which has its center fixed between the pair of plates 34 and 35. The attached end of operating rod 32 may be spun over to lock the plates tightly together with the diaphragm 38 in-between. The peripheral edge of diaphragm 38 is sandwiched between the flange rim 40 of a spring cup housing 42 and carburetor body 10. Rim 40 is tightly fastened as by machine screws 41, for example, extending through the housing flange 40 into the adjacent portion of the carburetor body 10. A spring 44 is mounted within the housing 42 with one end abutting the closed end of the housing and its other end biased into contact with the center of plate 35 of the diaphragm assembly. Spring 44 biases the diaphragm assembly 30 in a direction to close the air valve 26.

Diaphragm 38 forms with cup housing 42 a chamber 43 and with body casting 10 a chamber 45. Chamber 43 is sealed except for an air passage 46 extending through the wall and the flange 40 of the spring housing 42 to join a second air passage 47 through the carbure- Air passage 47 connects into a branch passage 49 having a restriction 49a which extends to a port 50 opening into the mixture conduit 17 between the closed position of throttle valve 21 and the air valve 26.

Formed within the body 10 of the carburetor are a pair of fuel bowls 52 and 54 (FIGURES 3, 4 and 6) positioned on opposite sides of the air horn structure 14. Fuel bowl 52 is adjacent to the mixing conduit 16 and fuel bowl 54 is adjacent to the mixing conduit 17. A fuel inlet passage 56 is formed through the body cover casting 19. As shown in FIGURE 3, the fuel passage 56 extends the length of the carburetor to provide fuel access to the two fuel bowls. The fuel passage 56 is connected in any appropriate manner to an inlet fuel line 58 leading from a fuel pump 60 which delivers fuel from a fuel tank 62. The fuel inlet line 58, fuel pump 60 and fuel tank 62 are only schematically shown in FIGURE 3.

Fuel from fuel passage 56 enters each fuel bowl through a short passage 61 having a valve seat, which is controlled by a needle valve 63 operated from a float lever 64 pivoted within each fuel bowl at 66 and having a free end attached to a float 68. The float controlled inlet needle 63 operates in a well-known manner. As the fuel in bowls -2 and 54 reaches a predetermined level, the floats 68 through levers 64 will force the pointed ends of needles 63 into the valve seats to prevent additional flow of fuel into the bowls, respectively.

In the bottom of each fuel bowl there is threaded a fuel jet 70 having a calibrated passage therethrough connected to a fuel passage 72 leading to a respective fuel well 74 or 75 (FIGURES 3 and 8) formed in the carburetor body and in the Wall of each of the mixing conduits 16 and 17, respectively. For example, in FIGURE 3 well 74 is indicated as being adjacent to the mixing conduit 16, and 75 is adjacent to mixing conduit 17. FIGURE 8 shows the well 74 and main fuel nozzle construction associated 'with mixing conduit 16, which is identical to similar structure associated with mixing conduit 17.

Mounted in the top of each one of the mixing conduits 16 and 17 is a separate subassembly insert 76 consisting of a pair of fuel tubes and the main nozzle structure. As shown in FIGURE 8, the subassemblies each consist of a block 78 having a tubular cross member 80 formed with a main fuel passage 82 and an idle fuel passage 84. Nozzle ports 83 through the wall of main fuel passages 82 allow fuel to pass into the mixture conduits 16 and 17, respectively. Press-fitted into one side of each sub-assembly block 78 is an apertured fuel tube 86 extending downwardly into the respective well 74 and 75. The upper end of each tube 86 is open and connects with the respective fuel passage 82. Coaxially mounted within each fuel tube 86 is an idle fuel tube 88, which is press-fitted in an upper portion of the respective block 78 with its upper open end connecting with the fuel passage 84. Fuel tubes 88 are closed except for a small restriction at their lower end suspended within the fuel wells 74 and 75, respectively. Short tubes are press-fitted into the opposite side of blocks 78 to form fuel passages leading from passages 84 across passages 82 into respective idle chambers 87. Idle chambers 87 open through ports upstream of the closed position of throttles 20 and 21, respectively. Short passages 93 connect idle chambers 87 to idle ports 97 opening downstream of throttles 20 and 21, respectively. Idle air and fuel flow through ports 97 is controlled by an idle adjusting screw 101.

Restrictions 89 of predetermined size form air bleed passages from the air horn section into air passages 90 leading into the upper portion of each well 74 and 75 to provide air flow into the main fuel passages. Air passages 91 extend from the upper end of the air horn through the fuel bowl cover casting 19 into air passages 92, each respectively connected to tube 85 and idle fuel passage 84. A restricted portion 94 in each passage 92 and restrictions 81 connecting idle passage 84 to the air horn 14 control the amount of air bled into the idle system.

Within each fuel bowl there is mounted a fuel metering rod 96, which is connected at an upper end to a lever 98 fixed to the portion of air valve shaft 28 extending over the top of each fuel bowl. The other end of each metering rod 96 has variations in rod thickness, as shown in FIGURE 7, consisting of an end portion 99 of minimum thickness, a tapered portion 103, an intermediate portion 100 of optimum thickness and a tapered portion 102 of varying thickness extending from portion, 100 to a minimum thickness portion 1105. The connection of metering rods 96 to the air valve shaft 28 provides simultaneous operation of the metering rods with the air valve. Metering rod 96 just described is more fully described and claimed in copending application of Forrest W. Cook and James T. Bickhaus, Serial No. 293,411, filed July 8, 1963.

A lever 104 (FIGURE 4) is fixed to the end of throttle shaft 22 opposite to that carrying throttle lever 24. Lever .104 carries a spring biased screw 104 for contacting a fast idle cam 106 freely pivoted on a screw shaft 108 and in an eccentric manner so that gravity will bias the cam 106 in a counterclockwise direction, as viewed in FIG- URE 4. A second lever 110 is :also freely mounted for rotation on screw shaft 108 and is connected by a link 112 to a control lever '1'14 fixed to a shaft 116 journaled for free rotation in a cup housing .118, as shown in FIG- URES 3 and 4. Control lever 114 is also connected by a link 119 to a lever 120 loosely mounted for rotation at one end of valve shaft 28. Fixed at the end of the air valve shaft 28 for rotational movement therewith is a short lever 1 22 having a portion 124 extending over the lever 120. In operation lever 14 operates to move in a counter-clockwise direction as will be described later and in making this movement the end 1:15 of link 1119 passes over center thus creating a toggle linkage between lever 1-14 and link 1 19. The aforementioned toggle linkage is more fully described and is claimed in copending application of Robert J. Smith, Serial No. 281,175, filed May 17, 1963.

Also fixed to an intermediate portion of shaft 116 for rotation therewith is a second lever 126 carrying at its free end a tapered metering valve .128. The upper end of valve .128 is pivotally mounted on the free end of a lever 126 so as to move relative thereto. The tapered end of the metering valve 128 extends into a restriction 130 having a pasage therethrough of predetermined size which leads into an air chamber 132 in the housing .118. Air chamber 132 is connected by an air passage 134 to short passage 136 joined to the air passage 47, as shown in FIGURE 5, and schematically indicated in FIGURES 1 and 2. The tapered metering valve 128 and its function is described and claimed in copending application of Forrest W. Cook, James T. Bickhaus and Robert J. Smith, Serial No. 276,472, filed April 29, 1963.

tent in the counterclockwise direction. In this position, the pivot 115 between levers 114 and 119 has passed over center of a straight line between shaft 116 and the pivot 117 between levers 119 and 120. A toggle link is formed by levers 114 and 119, as seen in FIGURE 2. This overcenter toggle condition retains the lever 12% in an uppermost position, where lever arm 124 will strike lever 120. This blocks open the air valve 26 and prevents it from closing when the engine is hot. Thus the engine can be started without an over-rich condition which would be provided with air valve 26 closed. An optimum opening for valve 26 for hot-engine starting conditions is from 25 to 30 degrees from its closed position. Also, holding the valve 26 in this open condition allows the engine when warm to function properly during idle operation and without an over-rich fuel mixture. In this blocked open position of the air valve, metering rod portions 100 are positioned within jets 70 to provide a sufficient flow of fuel to the engine.

As the engine cools when not running, the thermostatic spring 142 tensions. The lever 114 will be rotated clockwise slowly and will break the toggle stop. The air valve is then closed as lever 120* is slowly rotated clockwise by the cooling of spring 142. When cold, the air valve 26 is closed and in position for a cold start, as described above.

Engine operation When the engine is running and the throttles are opened from their closed positions, the air pressure at port 50 drops from atmospheric and the air pressure in motor chamber 43 is reduced until diaphragm 36 is pressed in wardly against the bias of spring 44. The air valve 26 then takes a position determined by servo motor 39, in which the difference in air force on the opposite sides of diaphragm 36 balances the bias of spring 44-. As throttles 20 and 21 are moved to change the amount of air flowing to the engine, the servo motor 39 will change the position of air valve 26 to retain substantially the same pres sure drop across the air valve. The air valve 26 is thus a device for measuring air flow through the carburetor to the engine.

The value of spring 44 is selected to retain a fixed pressure drop across the air valve. This spring sets the angular position of the air valve relative to the amount of air flowing through the carburetor. This then positions the proper portions of metering rods 96 within jets 70. The shape of metering portions of rods 96 are calibrated to give sufficient fuel flow through jets '70 to provide maximum power at any speed of the engine at wide open throttle up to the full air capacity of the carburetor.

The tapered portions 102 of metering rods 96 are shaped to provide an increasing flow of fuel through jets 70 as the air valve opens from its blocked open position to full open position, at which opening of the air valve, the rod portions 105 are within jets 70 for maximum fuel flow. The optimum air-fuel ratio is maintained with a full open air valve by the increased depression around the nozzle bars 80 due to increased manifold vacuum at higher speeds.

The air valve opening and metering rod position for a given air flow through the carburetor at wide open throttle operation will not provide the proper air-fuel mixture at part open throttle with minimum loads. It is thus necessary to change the relationship between the air flow through the carburetor and the flow of metered fuel to the engine, so that less fuel will flow during part throttle, minimum load conditions than during wide open throttle maximum power conditions.

Therefore, in accordance with our invention, means are provided whereby the servo motor 39 senses the high vacu urn conditions present during part throttle operation to cut down the flow of fuel to the engine. This effect is produced by the provision of a bleed passage 48 connecting air passage 47 to a port 51 in the mixture passage 17 downstream of throttle 21. This passage 48 reduces the air pressure in passage 47 and motor chamber 43 so that the air valve 26 is moved against spring 44 to a more open position than it would otherwise have. This raises the air pressure in the region of the nozzle bars 80, which reduces fuel flow from the nozzle apertures 83 to prdouce a leaner air and fuel mixture. Although opening of the air valve in this manner increases the open areas between the rod portions 102 and jets 70, the increase of air pressure around the nozzle bars has the controlling effect on fuel flow under the conditions described. Air bleed 48 is only effective under conditions of high manifold vacuum operation of the engine when economy of operation is desirable at low speeds or minimum load conditions. To provide the desired increase in the opening of air valve 26, a restriction is placed in the bleed passage 48. The size of the orifice in restriction 170 is preselected to give the desired effect. In a carburetor of the type described, a restriction of 0.035 inch was used. This opening size provided a correction to the position of the air valve proportional to the vacuum changes downstream of the throttle and sufficient to provide the desired air-fuel mixture for economy operation, as described.

An additional bypass passage 172 may be used extending from the air horn 14 to a port 174 in the mixture conduit 17 downstream of the throttle 21. In cold engine operation, passage 172 is closed, as shown in FIGURE 1, by a valve 176 controlled by a bimetal, temperature responsive spring 178. During hot ambient conditions spring 178 opens valve 176 and air can flow through passage 172 to lean out the idle mixture in the manifold.

We claim:

1. A carburetor comprising a body structure having an air and fuel mixture conduit therethrough,

(1) a throttle valve mounted across said mixture conduit for movement from an open position to a position closing said mixture conduit (2) means for operating said throttle valve (3) an air valve mounted within said mixture conduit anteriorly of said throttle valve for movement from an open to a position closing said mixture conduit, said air valve being eccentrically mounted for rotational movement on a shaft extending across said mixture conduit (4) means for supplying fuel to said mixture conduit between said air valve and said throttle valve (5) a servo motor connected to said air valve to move said air valve in response to pressure sensed within said mixture conduit (6) said servo motor including a sealed chamber having one movable wall connected to said air valve, spring means in said chamber normally moving said movable wall in a direction to urge said air valve toward closed position, an air passage connected at one end to said chamber and extending through the wall of said chamber, said air passage at its opposite end including branch passages, one of which is connected to said fuel mixture conduit above said throttle when the latter is in closed position, and the other branch passage being connected to the fuel mixture conduit below said throttle when in its closed position, said branch passages being provided with restricted areas, and an additional restriction in said air passage between its junction with the branch passages and the sealed chamber, whereby said movable wall of said chamber is urged against the action of said spring in response to pressure drop across said throttle valve to actuate said air valve toward open position,

(7) said air valve by way of its eccentric mounting being responsive to mass flow of air past said air valve and being positioned by the combined action of said servo motor and said mass flow of air.

2. The structure of claim 1 characterized in that the means for supplying fuel to said mixture conduit between 3116 a r valve and the throttle valve includes a metering pin A third lever 138 is fixed at the other end of the shaft 116'for rotation therewith. Lever 138 is bifurcated at its free end 140 to receive one end of a bimetallic thermostatic spring 142 fitted into the bifurcation 140 so as to move the lever 138. This connection is schematically shown in FIGURES 1 and 2. The other end of spring 142 is fixed to a stationary shaft 143 mounted on the cup housing 1'18.

The cup housing 118 is divided into a pair of chambers 145 .and 146 by an imperforate wall structure 144 extending transversely across the housing. This wall 144 prevents the interference of air flowing through one chamher with the air flowing through the other chamber. Chamber 145 is connected to the atmosphere through a vent schematically indicated at 147 in FIGURES 1 and 2. Chamber 146 is connected to a .source of heated air such as a stove connected to the exhaust manifold of the engine. Air from the stove is brought through the hot air conduit and through an inlet fitting 1148 into the chamber .146. Chamber 146 is connected by an air passage 149 to the carburetor flange 12 at a point downstream of the throttle '21. This is schematically shown in FIGURES 1 and 2 and in specific detail in FIGURE 5.

Because of subatmospheric air pressure condition in the manifold 13 during engine operation, air will flow from the manifold stove through the hot air conduit and fitting 148 into the chamber 1146 and from the chamber through passage 149 into the manifold. Also, when the valve 128 is open atmospheric air will flow through vent 147 into chamber .145 and from chamber 145 through passages 132, 134 and .136 into passage 47.

An accelerating pump piston 150 is mounted within a pump cylinder 152 (FIGURES 1 and 6) formed at the end of the fuel bowl 54. A one-way ball check valve 154 permits fuel to flow from the fuel chamber into the pump cylinder 152. The piston rod 156 is connected by a linkage 158 pivoted on the cover casting I19 through a link .160 to the throttle lever 24. The accelerating pump provides additional fuel during the opening of the throttle. When the throttle is opened, the pump piston 150 is pressed downwardly to force fuel through an accelerating fuel passage 162 connected to accelerating nozzles 164 (FIGURES 1 and 8) extending into each of the mixture conduits 16 and 17. This provides additional fuel during throttle operation.

In operation, the engine is cranked to openate the fuel pump and to force fuel into the inlet passage 56 of the carburetor. With the float valves in a lowered position, fuel will flow from fuel passage 56 into each of the fuel bowls 54 and 52. Fuel will continue to flow until the floats 68 are raised to a predetermined position, at which point the needle valves 63 are closed to prevent further flow of fuel int-o the fuel bowl. Fuel will flow from each bowl by gravity through the corresponding metering jet into fuel passages 72 and to a level in each of the fuel wells 74 and 75 equal to the level of fuel in the respective fuel bowl. Fuel will also flow past the check valve 154 to fill the accelerating pump cylinder 152 to the level of fuel in the fuel bowl.

One side of diaphragm 36 of the servo motor 39 is exposed to air pressure within chamber 43, which is connected to port 50 in mixture conduit 17 between air valve 26 and throttle valve 21. The other side of diaphragm 36 is exposed through passage 33 to substantially atmospheric air pressure in the air horn 14 upstream of air valve 26.

Starting During cranking of the engine with the throttle open, the engine turns over to pump air through the carburetor to start the engine. With the engine cold, spring 44 of the servo motor holds air valve 26 closed and the metering rods 96 at their uppermost position. This places the small diameter starting portions 99 of the metering rods respectively within the metering jets 70 and a rich flow of fuel will pass into the fuel nozzles 80. Sufiicient air to start the engine passes through apertures 25 and 27 in the air valve 26 and into the mixture passages 16 and 17, respectively. Fuel to start the engine is drawn out of the fuel wells 74 and 75 and the nozzle bar passages 82 and 84 by the manifold vacuum extending upstream of the open throttles to the nozzle bars 80. This fuel passes into the mixture conduits through the main nozzle ports 83 and the idle ports and 97.

Cold engine operation When ambient conditions are below a temperature of about 75 F., the thermostatic spring 142 biases lever 138, shaft 116 and lever 114 in a clockwise direction to a position, shown in FIGURES 1 and 4. In this position, operating lever 114 and link 112 have moved the fast idle cam 106 in a clockwise direction against gravity bias by the aid of a lug 109 fixed to lever 110 in the path of rotation of cam 106. After the engine has started and the throttle lever 24 manually released, the adjustment screw stop 104' on the throttle lever 104 will contact the high portion 107 of the cam 106 and hold the throttles in a slightly open position so the engine will operate at a fast idle speed. The idle speed of the engine provides a subatmospheric pressure within the intake manifold opening 18 in the order of 18 to 20 inches of mercury negative pressure. This negative pressure will be effective upstream of throttles 20 and 21 to cause a depression below air valve 26. This low pressure will be sensed through port 50 and passage 47 to the servo motor 39, which will operate to partially open the air valve 26 and permit flow of sufiicient air past throttles 20 and 21 for the cold idle operation.

Idle fuel is drawn from the nozzle ports 83. Also, air passing through apertures 25 and 27 will sweep around the upper edges of the slightly open throttles 20 and 21 and will draw air and fuel from the idle ports 95. The metering rod portions 103 are positioned within jets 70 during this cold engine idling operation.

Under cold-engine operation, with shaft 116 biased by spring 142 to its position shown in FIGURES 1 and 4, the metering valve pin 128 is out of the air restriction 130 so as to provide a bleeding of air through passages 134 and 136 to passage 47 and through passage 49 to the mixture conduit. This air bleed slightly increases the pressure within the servo motor chamber 43 which, with the spring 44, closes the air valve 26 slightly from a position it would otherwise have. This results in a higher depression area between the air valve and throttles 20 and 21 which induces a richer fuel flow from the nozzle ports 83 and optimum engine performance for cold engine operation. The amount that valve 26 is closed by the air bled through passages 134 and 136 may be adjustably controlled by the size of a restriction 135 placed in passage 47 between passages 136 and passage 49. This restriction may be in the range of 0.025" to 0.040" in diameter to provide the desired effect.

When the engine has warmed to a normal operating temperature, thermostatic spring 142 has rotated shaft 116 and levers 114 and 110 to their positions indicated in FIGURE 2. When the throttles are now operated, the idle stop screw 104' releases the fast idle cam 106 and permits it to drop by gravity. If the throttles are subsequently released for idling conditions, the screw 104' will contact the lowest cam position 107a (FIGURE 4) and allow the throttles to take a closed position. Idle fuel is now drawn by manifold vacuum mainly from the idle chamber 87 through the idle port 97 and in the manner described above. Air flows through idle bleeds 81 and 91 and the bypass passage 163 controlled by the adjustment screw 165.

Rotation of shaft 116 by spring 142 counterclockwise, as viewed in the figures, moves valve needle 128 into orifice 130 to close off the air bleed to passage 47 and eliminate the fuel enrichening effect of this bleed. Simultaneously, operating lever 114 is rotated to the fullest ex- References Cited by the Examiner UNITED STATES PATENTS 4/1932 Capell 26150 4/1961 Rapplean et a1, 261-39 X Mick 26139 X Mick 26139 X Mick 2615O X Hamilton 26139 Mennesson 26150 X FOREIGN PATENTS Great Britain.

10 HARRY B. THORNTON, Primary Examiner.

T. R. MILES, Assistant Examiner. 

1. A CARBURETOR COMPRISING A BODY STRUCTURE HAVING AN AIR AND FUEL MIXTURE CONDUIT THERETHROUGH, (1) A THROTTLE VALVE MOUNTED ACROSS SAID MIXTURE CONDUIT FOR MOVEMENT FROM AN OPEN POSITION TO A POSITION CLOSING SAID MIXTURE CONDUIT (2) MEANS FOR OPERATING SAID THROTTLE VALVE (3) AN AIR VALVE MOUNTED WITHIN SAID MIXTURE CONDUIT ANTERIORLY OF SAID THROTTLE VALVE FOR MOVEMENT FROM AN OPEN TO A POSITION CLOSING SAI D MIXTURE CONDUIT, SAID AIR VALVE BEING ECCENTRICALLY MOUNTED FOR ROTATIONAL MOVEMENT ON A SHAFT EXTENDING ACROSS SAID MIXTURE CONDUIT (4) MEANS FOR SUPPLYING FUEL TO SAID MIXTURE CONDUIT BETWEEN SAID AIR VALVE AND SAID THROTTLE VALVE (5) A SERVO MOTOR CONNECTED TO SAID AIR VALVE TO MOVE SAID AIR VALVE IN RESPONSE TO PRESSURE SENSED WITHIN SAID MIXTURE CONDUIT (6) SAID SERVO MOTOR INCLUDING A SEALED CHAMBER HAVING ONE MOVABLE WALL CONNECTED TO SAID AIR VALVE, SPRING MEANS IN SAID CHAMBER NORMALLY MOVING SAID MOVABLE WALL IN A DIRECTION TO URGE SAID AIR VALVE TOWARD CLOSED POSITION, AN AIR PASSAGE CONNECTED AT ONE END TO SAID CHAMBER AND EXTENDING THROUGH THE WALL OF SAID CHAMBER, SAID AIR PASSAGE AT ITS OPPOSITE END INCLUDING BRANCH PASSAGES, ONE OF WHICH IS CONNECTED TO SAID FUEL MIXTURE CONDUIT ABOVE SAID THROTTLE WHEN THE LATTER IS IN CLOSED POSITION, AND THE OTHER BRANCH PASSAGE BEING CONNECTED TO THE FUEL MIXTURE CONDUIT BELOW SAID THROTTLE WHEN IN ITS CLOSED POSI- 